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Modernized Wastewater Pre-Treatment at Bulgarian Paper Mill

Two ROTAMAT® rotary drum fine screens Ro 2 and grit washer RoSF 4

Two outdated coarse bar screens at the paper mill were replaced

The paper mill of Duropack-Trakia Papir AG is located in Pazardzhik, a town located in central Bulgaria with a population of over 80,000 inhabitants. The paper mill has an own wastewater treatment plant.

Wastewater Pre-treatment at the paper mill was done until recently with a pair of ancient and decrepit bar screens of local manufacture. The old bar screens had a bar spacing of 25 mm and did no longer perform sufficiently. Operation and maintenance were troublesome, labour-intensive and costly. The removed screenings were wet and their disposal very expensive. Since the screens were very coarse, a large amount of solids passed through and lead to increased wear and maintenance at downstream equipment and processes. The grit separated in their grit chamber is wet and odorous, it contains many organic solids, and its disposal is increasingly expensive.

The management of the paper mill wanted to reduce the operating costs of their wastewater treatment plant. They identified that a major portion of their operating costs resulted from the inefficiency of their outdated screens. They decided to have the screens replaced with state-of-the-art equipment. Their main objective was minimizing the mass of their grit and screenings in order to minimize disposal costs. The management also required that the new screens should fit in their existing channels; and the entire new equipment for screenings and grit treatment should fit into their existing building. To make it even more challenging, the entire refurbishment had to be performed while the paper mill and its wastewater treatment plant remained in full operation. Fast exchange, installation and start-up of the equipment were therefore necessary.

Engineers of Huber Technology Bulgaria, the local subsidiary of Hans Huber AG, offered two Ro 2 Rotary Drum Fine Screens with a 1,200 mm drum diameter and a wedge wire spacing of 1 mm. These ROTAMAT® screens fit easily into the existing channels. Each screen has a 500 m³/h hydraulic capacity, which is the same as the plant’s peak flow, so that two screens offer 100 percent redundancy. Of course these very fine screens remove far more solids from the wastewater than the former coarse screens did, but the ROTAMAT screens have an integrated screenings wash-press. They compact the screenings to a solids concentration of 30 – 35 %. Because of their far reduced water content, the volume of the screenings is far lower than before.

We also offered a COANDA grit washer RoSF 4, size 1, for grit treatment. The HUBER grit washer is peerless because it combines excellent product cleanliness and dryness (< 3 % of volatiles and < 10 % of water in the washed grit product) with an excellent grit capture rate (> 95 % of grit particles with a diameter of 0.2 mm). The washed grit is so clean that it can be reused as construction material.

The customer’s decision to select our equipment was based on the following criteria: High operational reliability, excellent performance in respect to capture rates and mass reductions, competitive pricing, low power and water consumption. Our equipment was successfully started-up on July 7, 2007.

Because our customers are happy with the operation and performance of our equipment, we are now in discussions with Duropack-Trakia Papir AG about further cooperation helping them to solve some other problems of their wastewater treatment plant.